It's about a company acting in a way that is alienating to its userbase. Now, many people might think retard is offensive and would prefer a sanitized environment... but many people don't. Saying "we disagree with what you did" is a way to the users to tell the company that they might be drifting away from what made them interesting in the first place.
You can be legal AND an asshole.
If every time your friend was being an asshole to you, he'd stop listening and said: "Well, it's legal.", he probably wouldn't be your friend for long.